1. Technical Field
This invention relates generally to the collection of solar energy for conversion into electrical energy, and more specifically to the arrangement of solar panel drive and tilt mechanisms to follow the movement of the sun relative to the earth. Still more specifically, the present invention relates to a drive mechanism for rotating a large array of solar panels in a cost effective manner.
2. Background Art
For years drive mechanisms have been employed to rotate and align solar panel arrays. However, most of the drive mechanisms in the prior art have not been designed to use a single drive unit to move large arrays with multiple rows of panels. Extremely large multi-megawatt solar power stations are now being planned and built, so the need for efficiently driving large arrays has become an important and necessary part of the solar power system.
In general, solar photovoltaic panels for large scale energy production comprise a collection of photovoltaic cells configured in rectangular patterns. A number of panels are typically mounted level with one another on top of support structures with minimal spacing between panels. This economizes on space and maximizes solar collection efficiency.
Further, solar panel arrays are typically mounted to optimize the sunlight striking their surfaces during daylight hours. In order to further improve solar collection efficiency, drive mechanisms have been employed to keep the panel surfaces in a perpendicular (normal) orientation relative to the direction of travel of the sun's rays.
There are a number of prior art drive systems designed to track the sun with a solar panel array. These drive mechanisms generally tilt the solar panel arrays by moving the structures upon which the panels are mounted. Both horizontal and vertically driven systems have been utilized for this purpose. Although numerous panel movement mechanisms have been employed, they are generally ill-suited for using a single drive system to rotate large arrays (i.e., those having 1000 or more panels). Accordingly, the installation and commissioning of large solar panel array tracking systems using such drive mechanisms have been complicated and therefore costly.
A number of patents show tilt mechanisms for the movement of multiple panel arrays. Notable examples include:
U.S. Pat. No. 4,429,178 to Pridaux et al (1984), which shows a plurality of closely spaced solar panels mounted in pairs on opposite sides of a number of horizontally extending, co-linear torque tubes supported for rotation about their respective co-linear axes by a number of support posts. A drive assembly on one of the support posts is connected to a pair of torque tubes for simultaneously rotating these and the other torque tubes in a solar tracking mode.
U.S. Pat. No. 5,228,924 to Barker et al (1993), discloses a mechanical solar module support structure for pivotally more than one photovoltaic panels in a planar array. The system uses a single mechanism to simultaneously change the angle of declination of the array by the same amount. The system includes at least two side-by-side coplanar panels, a pivot shaft extending transversely of the side-by-side panels, at least two supports spaced apart lengthwise of the shaft, mounting apparatus for mounting the pivot shaft to the supports, connectors for connecting the panels to the pivot shaft so that the panels can pivot about the longitudinal axis of the shaft, a mechanical coupling linking the panels together to form a unified flat array, and a drive motor for mechanically pivoting the unified array about the axis and for locking the array against pivotal movement when the motor is off.
The systems shown in each of the '924 and the patents depend on a single spine to pivot and support the solar panels. This necessitates additional structural cross-members to provide adequate support for the panel arrays due to gravity and to withstand high winds. The additional cross-members increase the spacing or height of the panels above the pivot axis. Consequently, the side forces on the panels due to wind loading create substantial torsional forces that must be withstood by the rotational drive mechanism, and this leads to a need for much higher drive forces.
U.S. Pat. No. 6,058,930, to Shingleton, teaches a drive mechanism for rotating solar arrays using a single torque tube. The disadvantage of this approach is that the torque tube and the bearings at the support posts must be quite large to transmit the torque. The '930 patent also teaches driving multiple rows of panels simultaneously utilizing a single ram drive mechanism. The problem with this approach is that the ram force required to drive a large number of panels creates a substantial side force at the ram base. This creates the need for substantial anchoring or large pedestals to withstand the large side load produced by the ram.
Another liability of prior art drive systems is that they create challenges for field installations. For instance, using the prior art systems, vertical adjustments of the arrays have been difficult and limited. This problem is most prevalent for arrays mounted in a soil environment where the main means of support is typically driven pilings. Because of the variations in piling heights it is necessary to provide vertical positioning and holding devices to adjust the solar panel arrays to the required height. This is a time consuming and expensive process. Screw adjustment mechanisms may be used. However, they are generally expensive for the large diameters needed for posts which supporting multiple panels.
In summary, the prior art drive mechanisms for rotating and tilting solar panels configured in a large array having multiple rows all suffer from a number of disadvantages, including: (a) the need to use expensive support structures for the large array; (b) deficiencies in adequately addressing the effect of wind on the forces required for array rotation; (c) deficiencies in addressing how to withstand large side loads generated by multiple row arrays; (d) expense; and (e) the need to use drive methods with large, exposed moving parts that can create hazards to personnel and equipment nearby.
The foregoing patents and other prior art devices reflect the current state of the art of which the present inventors are aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicants' acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.